This invention relates to a valve assembly generally used to control a vacuum motor in response to a vacuum or pressure signal from a monitored source. More specifically, this invention relates to a vacuum operated control system that utilizes a trapped vacuum which gradually decays through an orifice or porous plug during the time that the vacuum output level is greater than the input vacuum level.
In an automobile, delay valves are utilized to control various functions, such as vacuum advance, blend-air doors, thermactor air management systems, and other applications. Delay valves suitable for idle speed control were disclosed and claimed in U.S. patent applications having Ser. Nos. 155,241 and 155,242, both filed on June 2, 1980, and assigned to the assignee of this invention. These prior art delay valves have decay curves graphically illustrating that the vacuum level in an output chamber is decreasing (or increasing in an input chamber) as a function of time, if the chamber is sealed from further vacuum input at a level equal to or greater than that of the output chamber. This decay function is often so slow as to inhibit rapid actuation of a controlled element, such as a carburetor or air injection system of a vehicle. Therefore, a principal consideration of the present invention is to allow a normal, smooth vacuum decay from the output chamber and then, at a predetermined vacuum level, to rapidly balance the input and output vacuum levels in such valves.
When such a delay valve is mounted in an automobile, the undesirably slow decay of the vacuum operated delay valve can inhibit successful completion of the controlled operation. In some instances, such slow decay can create a secondary problem, such as the production of a resonant frequency effect in the controlled system which degrades the desired controlled operation and thus may produce mechanical noise or inhibit emission control.